Resistor for electric furnaces



Deb. 30, 1924. 1,521,028

G. M. LITTLE RESISTOR FOB ELECTRIC FURNACES iled May 24,, 1921 INVENTORMZM BY 1/777 M M/u Patented Dec. 30, 1924.

UNITED STATES PATENT OFFICE.

GEORGE m. LITTLE, OF PITTSBURGH, PENNSYLVANIA. ASSIGNOR TO WESTINGHOUSEELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

nnsrsron ron ELEICTRIC FURNACES.

Application filed May 24, 1921. Serial ms. 472,094.

'1 '0 all whom it may concern:

Be it known that I, Gnoaon M. LrrrLE, a citizen of the United States,and a resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in Resistorsfor Electric Furnaces, of which the followingais a specification. a yinvention relates to electric furnaces and particularly toelectric-resistance furnaces and it has for its object to provide acombination electric-furnace resistor -comprising carbonaceous platesand granular carbonaceous material.

"In my co-pendin application, Serial N o. 454,776,filed Marc 23, 1921, Ihave disclosed a resistance type of furnace in which the resistorconsists of a plurality of relatively thin carbonaceous plates which areresiliently pressed against each other. The resistance of such aresistor element-is rela: tively low, so that, in order to obtain therequiredheating 'efi'ect, it is necessary to pro? videa source ofelectric energy of relatively low voltage and of high vcurrent capacity.The energy loss in the contact terminals and in the leads between theterminals of the furnace and the transformer or the controlpanel are,therefore, relatively high.

In practicing my invention, I provide a resistor element comprising aplurality of carbonaceous plates which are maintained in spaced-apartrelation by interposing between two adjacent plates a thin layer ofgranular carbonaceous material or a plurality of relatively smallcarbonaceous plates. The built-up resistor element described above isresiliently compressed by suitable means andmaintained in its operativeposition in the furnace chamber by the same, compressing means; I

In the single sheet of drawings: Figure 11s a view, in verticalcross-sec tion, of an electric-resistance furnace com-,

prising the device embodying my invention: 1 Fig. 2. IS a view, invertical cross-section of an electric resistance furnace comprising amodification of the device embodying my .invention, and 7 Fig. 3 1s aview, in perspective, of one elesurface.

work 11, provided with suitablesupporting members 12. Outerwulls 13comprise a plurality of bricks or blocks of any suitable heat-insulatingmaterial. Inner' walls 14 comprise a plurality of bricks or blocks ofany suitable high-tcmperature-resisting' material. The inner walls aresuitably spaced. apart to form a furnace chamber 15 of any suitable ordesired contour and dimensions.

As this type of vfurnace is intendedto be employed .for heating--metallic objects, a suitable opening 16- is provided near the bottomof the furnace chamber through which the materials to be heated may beinserted andremoved. 1;

A resistor located in the chamber 15 comprises a p'luralityofcarbonaceous plates 17.

In the modification illustratedin Figure 1, the adjacent plates 1-? arespaced apart a short distance by means of a layer of man- .lar carbon.To cause the gnmular car on to adhere to a plate, itis only necessary topaint one of the. flatsurfaces. of each plate with a thin layer ofadhesive, such as deli trine, and sift a thin layer of granular-carbon.on this layer of adhesive. After a sufiicie'nt number of plates havebeen this repared, they may be stacked. toget er,

clamped, and then dried by; the apphcation of heat, after which theresistor. is ready to be placed in the furnace chamber.

In order to provide a proper'ter al for each end of the resistor, thegraphite plate .18 is located at each end ofthe-resistor and is providedwith a depression in its outer An electrode 19 oonsistin of-carbonaceousmaterial is provided, the inner end of which is adapted to operativelyem. gage the depression in the graphite member 18. The electrode19 maybe substantially circular'in lateral cross-section and relative- 'lyelongated to extend outwardly through the wall of the furnace.

A water-cooled metallic. contact terminal 20 is mounted ontheouter endof the electrode 19, and is provided with a central air erture 21,substantially conical in form to fit No. 464,290, filed April 25, 1921.It may be on the tapering outer end of the electrode noted that the areaof contact of a grain of 19. the granular carbonaceous material with theResilient compressing means are provided plate 17 may be relatively verysmall, and, and comprise an adjustable screw 22 and a in some cases, mayeven form a point conhelical spring 23, one end of which is tact. If anysoot is deposited around this pressed against the outer end of thecontact grain of. material, the area of contact beterminal 20, aninsulatin r member 24 being tween it' and the adjacent plate will beinplacedbetween the end 0 the spring 23 and creased to a veryappreciable extent, thus, of

the contact terminal 20 to roperly insulat e course, decreasing theresistance of the rethe two members from eac otherQ It is to i'sistorelement. be understood that the resilient compress- By making the areaof the small plates 28 ing means, as illustrated, is schematic onlyrelatively small, 'as compared to the area of and that any suitable ordesired resilient the plate 17., the resistance of such a built-upcompressin means may be employed.

An annu ar member 25, which may conor even greater han, that of thecombined 'sist of asbestos, is placed around the contact plate andgranular carbonaceous material,

terminal 20 to effectively insulate this terand the efi'ect of sootdeposited around the.

minal from the small plates 28 is not as great as is the case furnace.when As the temperature of the electrode is used; ence, the resistanceis not reduced relatively very high at itsinner end where as much as inthe modification illustrated in it engages the graphite member 18 andmay Fig. 1 be almost as hot in the walls 13 and 14,1 It may be notedthat I have illustrated a provide means for preventing the oxidationsingle built-up resistor element so that the of this heated electrode byair which may two terminal electrodes are located on oppometallicframework of the resistor may be ade substantially equal to,

ranular carbonaceous material is leak past the contact terminal 20. Thissite walls of the furnace but this is not essen means comprises a wellor hopper 26 in tial and I may use two parallel resistonelewhich islocated a mass 27 of granularcar: merits, each one resiliently pressedagainst bonaceous material which may be tightly ne sidewall of thefurnace, the two tar-- tamped in place around the electrode 19. minalelectrodes being, therefore located in Further description of this partof the furone sidewall of. th'efurnace. nace is believed unnecessary,inasmuch as it an essential element of my invention, howconstitutes thesubject of my co-pending ap ever, and in nowise affects the inventiveplication Serial No. 472,093, filed May 24, idea. I

1921. It may be noted that the device embodying In the modificationillustrated in 2, my invention provides a relatively simple This is notthe means for separating the adjacent plates uil -up IeSiStOI w ic has ga 17 comprise a pluralityof plates 28 of carsistance than the resistorbuilt up onl of bonaceous material of relatively small area. flat platesand that this resistor is relativelv' These plates may be caused toadhere to the inexpensive and easy to make. The higher flat surface ofthe plate 17 by substantially inherent resistance permits the use of athe same means as hercinbefore described in smaller current to obtainthe same heating connection with the resistor illustrated in effect asis obtained with a built-up carbon- Fig. 1. The modified form ofresistor illusp e resistor he etofore used. irated in Figs. 2 and 3 hasan advantage over Various modifications may be made in the thatillustrated in Fig- 1, in that the thickdevice embodying my inventionwithout dencss of the means spacingapart the adjaparting from the s iritand scope thereof cent plates 17 are more uniform in thickness. and Idesire that on y such limitations shall This is of advantage inpreventing breakage be placed thereon as are imposed by the prior of theplates 17 when they are compressed art or are specifically set forth inthe apby the resilient compressing means hereinpended claims. beforedescribed. I claim as my invention:

I have found that, while the resistance of the resistor illustrated inFig. 1 is relatively a plurality of thin flat plates of refractory highat the beginning, it decreases a relamaterial, means comprising granularelectively large amount in the first few days of trio-conductingmaterial for electrically conits use and I attribute this result to theacnecting said plates-over. only a relatively tion of the sooty vaporwhich I use in fursmall portion of their area, said means servnaces ofthis type to protect the carbonaceous in also to maintainsaid plates insubstan resistor against the oxidizing effect of air tia ly spaced-apartrelation, and means for entering the opening 16. Means forpromaintaining said resistor under substanducing such a sooty va por aredescribed and tially constant compression.

claimed in my co-peud mg ipplication Serial 2. In an electric furnace, aplurality of 1. An electric furnace resistor comprising furnace wallsenclosing a furnace chamber, their area and for spacing said successivea resistor in said chamber comprising a plates apart, and means forholding said plurality of thin flat plates of refractory resistor insaid chamber free of said walls. electrical-conducting material,refractory In testimony whereof, I have hereunto 5 granularelectrical-conducting means for subscribed my name this 18th day of Mayconnecting the Hat surfaces of ad'acent 1921. plates over only arelatively small portion of GEORGE M. LITTLE'

